1. Technical Field
The present invention relates to a method of determining the appropriateness of satellite orbit modeling, a method of providing long-term predicted orbit data, and a device for determining the appropriateness of satellite orbit modeling.
2. Related Art
A GPS (global positioning system) is widely known as a positioning system using a positioning signal and is used for a positioning device built in a mobile phone, a car navigation apparatus, or the like. The GPS measures the position by executing a positioning operation for calculating four parameter values of three-dimensional coordinate values, which indicate the position of a GPS positioning device, and a time error on the basis of the information, such as the positions of a plurality of GPS satellites or a pseudo distance from each GPS satellite to the GPS positioning device.
In positioning using the GPS, satellite information including the position, speed, and moving direction of the GPS satellite is calculated on the basis of the navigation data, which are called the almanac or ephemeris, and are superimposed on the GPS satellite signals transmitted from the GPS satellite and the positioning operation is performed using the satellite information and time information. In particular, the ephemeris serves as an important key when acquiring the satellite. Accordingly, for example, when positioning starts in a state where the ephemeris is not stored, the time to first fix (TTFF) is increased. In addition, even if it is not a first positioning, the acquisition time changes a lot according to whether or not the ephemeris of the satellite is stored when acquiring a certain satellite for the first time.
For this reason, International Publication No. 2006/031652 pamphlet discloses the technique in which the server in the server-client system predicts the ephemeris for a long period of time of one week and provides the predicted ephemeris (hereinafter, referred to as the long-term prediction ephemeris (long-term predicted orbit data)) to the positioning device which is the client.
A method of defining the long-term prediction ephemeris in the same data format as the normal ephemeris may be considered as a method of defining a long-term prediction ephemeris. It is a method in which the satellite orbit is approximated using the Kepler's elliptical orbit model, which is one of the approximate models of the satellite orbit, and the long-term prediction ephemeris is defined by a parameter value (hereinafter, referred to as a satellite orbit parameter) of the model at that time. The satellite prediction calendar (predicted position data) including the predicted positions, which are obtained by predicting the future positions of the positioning satellite in time series at predetermined intervals, is provided from a predetermined commercial system. The approximate calculation based on the Kepler's elliptical orbit mode
However, in the predicted positions stored in the satellite prediction calendar, the predicted position which is extremely (several kilometers) distant from an adjacent predicted position in positional relationship with the adjacent predicted position may be included as a so-called abnormal value. Ideal approximation of the satellite orbit is the elliptical orbit in which all predicted positions are correctly reproduced. However, when the abnormal value is included, the elliptical shape is distorted due to the abnormal value. In the case of a distorted satellite orbit, it is natural that the reproducibility of the predicted position is not good.